What's funny is when I ask what antivirus I should use and they tell me "Defender" and MalwareByte. I also installed Spybot et MalwareByte even tho I deactivate their respective real-time capabilities (I just use them to analyze my computer once in a while). So if the algorithm contains a bug that triggers in very specific situations on very specific machines, there will always be someone with a problem at some point. For what I understand by being an engineer that had to learn the basics of computer security, it's pretty much inevitable to consume resources to protect and analyze a machine. I've actually seen that on some of my friends computers but they were using AVG or Avira so yeah. I've heard it can sometime consume a lot of resources, but I've heard that for EVERY ANTIVIRUS EVER at some point. It blocked a lot of shaddy websites and infected ads. I like the startup analyze that you can trigger before the system to analyze the whole machine without interference.
It can sometimes put things in quarantine that are not viruses (like the program I just compiled on my computer with my code in it. And right now if you just ignore the ads and tell it to shut the F up and do its work, it doesn't bother me at all. I've seen McAfee, Norton, MalwareByte and some others that tried to get themselves installed like malwares but I've never seen Avast do that. Some even say that it was installed on some computers like malwares. I heard they sold personal information at some point, like if Microsoft, Google Chrome and other don't do that already. I mean yeah it really like to tell me I'm insecure and that I need to pay for protection (but so far I haven't seen any antivirus NOT do that). Uninstalling it NEVER solved any of my problems. It happened a lot of times already and I can understand why some people don't like Avast, but I've never had problems with it in the past. The thing is that, once again, the moment they saw I had Avast as my antivirus, they got NUTS and begged me to uninstall it like it was some kind of mutated plagued alien monster that needs to be burnt to ashes and the ashes burnt again. I asked for help on forums and received some classic diagnostic and "cleaning" advises (like I did not tried that already but it's always good to ask).
I've recently had problems with my computer when I installed Windows 11 (but that's not the subject).